Introduction to TypeScript for Java Engineers (Part 3: Primitive Types)

Information

To reach a broader audience, this article has been translated from Japanese.
You can find the original version here.

Introduction

This time, we will explain primitive types.

Name, Overview	JavaScript	TypeScript	Java
Numbers (integers, decimals)	number	number	int, long, float, double
Numbers (large integers)	bigint	bigint	≒BigInteger
Strings	string	string	String
Boolean values	boolean	boolean	boolean
Symbol type	symbol	symbol	-
Null value	any	null	≒null (no definition as a type)
Undefined value	undefined	undefined	≒null (no strict concept of undefined)

The table maps TypeScript types to similar types.

number (Numeric Type)

A type that handles 64-bit floating-point numbers, capable of representing both integers and floating points.

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let num1: number = 1000;
let num2: number = 1000.5;
let num3: number = .5; //0.5
let num4: number = -1000;
let num5_p: number = Number.POSITIVE_INFINITY; //Infinity positive infinity
let num5_n: number = Number.NEGATIVE_INFINITY; //-Infinity negative infinity
let num6: number = parseInt("hoge"); //*1
let numInf = 1000; //*2

1: NaN is set without throwing an exception
2: Determined to be of type number by type inference

How it works in Java

int num1 = 1000;
double num2 = 1000.5;
double num3 = .5;
int num4 = -1000;
double num5_p = Double.POSITIVE_INFINITY;
double num5_n = Double.NEGATIVE_INFINITY;
//int num6 = Long.parseLong("hoge"); //*1
var numInf = 1000;

1: Doing similar results in a NumberFormatException being thrown
2: Determined to be of type int by type inference

bigint (BigInt Type)

A type that can represent integers larger than those handled by number.
The assigned value is expressed by appending n to the end.
When using it, the compiler option target must be set to es2020 or higher. (Otherwise, it will result in a compilation error)

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2023",
  }
}

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let bi1: bigint = 1000n; //1000
let bi2: bigint = BigInt(1001); //1001
let bi3: bigint = BigInt("1002"); //1002
let bi4: bigint = -1000n; //-1000
// let bi5: bigint = -1.1n; //Error because it's a decimal
let biInf = 1003n; //*1

1: Determined to be of type number by type inference

How it works in Java

// BigInteger bi1 = 1000;
BigInteger bi2 = BigInteger.valueOf(1001);
BigInteger bi3 = BigInteger.valueOf(Long.valueOf("1002"));
BigInteger bi4 = BigInteger.valueOf(-1000);
// let bi5: bigint = -1.1n; //Error because it's a decimal
var biInf = BigInteger.valueOf(1003);

1: Determined to be of type BigInteger by type inference

string (String Type)

A type that handles strings.

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let str1: string = "hoge";
let strInf = "fuga"; //*1

1: Determined to be of type string by type inference

How it works in Java

String str1 = "hoge";
var strInf = "fuga"; //*1

1: Determined to be of type String by type inference

boolean (Boolean Type)

A type that handles true and false.

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let bool1: boolean = true;
let boolInf = false;//*1

1: Determined to be of type boolean by type inference

How it works in Java

boolean bool1 = true;
var boolInf = false; //*1

1: Determined to be of type boolean by type inference

symbol (Symbol Type)

A type that generates unique values.

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let symbol1: symbol = Symbol(); //description=undefined
let symbol2: symbol = Symbol("sym-value"); //description=sym-value
let symbol3: symbol = Symbol(); //symbol1==symbol3:false, symbol1===symbol3:false *1
let obj1 = { [symbol1]: "value1", symbol2: "value2" }; //obj1[symbol1]=value1, obj1.symbol2=value2
let symbolInf = Symbol(); //*2

1: They do not match because each is unique
2: Determined to be of type symbol by type inference

How it works in Java

// There is no corresponding type.

To express something similar, you need to create your own mechanism.

null

A type that indicates the absence of a value.

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let null1: null = null;
let nullInf = null; //*1

1: Determined to be of type null by type inference.

How it works in Java

// Null values exist, but there is no null type.

interface BaseCustomType {}
static class CustomType implements BaseCustomType {}
static class CustomTypeNullObject implements BaseCustomType {}

Optional<String> null1 = Optional.empty();
var nullInf = new CustomTypeNullObject();

Using Optional or the Null Object pattern can express something similar.

undefined

A type that indicates an undefined state.

Characteristics of the Type

Let's confirm the characteristics of the type through code.

TypeScript

let undef1; //undefined *1
let undef2: undefined; //undefined
let undef3 = undefined; //undefined *1

1: Determined to be of type undefined by type inference

How it works in Java

// There is no strict concept of undefined.

Using the Null Object pattern can express something similar.
The implementation example is the same as for Null, so it is omitted.